Electrochemical sensors are known which typically comprise three electrodes in contact with an electrolyte. These electrodes are normally identified as a working electrode, a counter electrode and a reference electrode. Generally speaking, in such sensors, the reference electrode is held at a constant potential with respect to the working electrode. The presence of substances which interact with the working electrode/electrolyte interface can invoke current flow between the working electrode and the counter electrode as a result of reduction/oxidation (REDOX) reactions at the working electrode. Other electrochemical sensors may only have a working electrode and a counter electrode and in such sensors the potential difference, current flow or resistance between those electrodes may be measured.
Generally speaking, such electrochemical sensors are made on a one by one basis or by using techniques that are quite variable. As a result, the sensors tend to vary from one to another. In some fields of use, such as carbon monoxide sensors, this is not too much of an issue as the trigger threshold for the associated electronics to issue an alarm is set so high that there can be no doubt that an unsafe level of carbon monoxide has been reached. However, for situations where greater precision and/or resolution are required then the sensors have to be calibrated prior to use. This is generally expensive and/or time consuming. Furthermore, it is generally desirable to reduce the size of sensors, in order to increase the range devices and applications with which they can be used.